This invention relates to postal scales and more particularly to battery powered postal scales.
Postal scales which determine the weight of an item to be mailed and compute the appropriate postage for that item in accordance with the weight and other postal information, such as destination and class of service, are well known in the art. One such postal scale system is taught in U.S. Pat. No. 4,286,325 to Dlugos, et al., for System and Method for Computing Domestic and International Postage; which is hereby incorporated by reference. Such scales are typically powered by an electronic power supply dispite the fact that, at least for smaller stand alone systems which do not incorporate a postage meter or printer or other peripherals which consume large amounts of power, the power needed might be more economically supplied from batteries. Users of small, stand alone postal scales and other such business equipment have been willing to pay the cost differential for electronic power supplies to avoid the problems and inconvenience associated with stocking and replacing or recharging batteries, and to avoid the possibility erroneous operation as the batteries run down. These problems are so burdensome to users that batteries are generally not used as main power sources except in equipment where portability or continued operation in the event of power interruption are necessary.
Another aspect of postal scales is that postage for an item to be mailed is computed in accordance with postal rate information provided by the United States Postal Service and/or the Postal Services of various other countries. The most economical way for this postal information to be incorporated into a small, stand alone postal scale, prior to this invention, has been through the use of programmable read only memories (PROM's). PROM's provide non-volatile data storage and are relatively easy for a postal scale vendor to program with new information such as postal rate change.
Such rates change too frequently and the postal scale market is too small for read only memories (ROM's), where data is incorporated into the ROM at the time of manufacture, to be economically feasible, and random access memories (RAM's) do not provide non-volatile storage unless a back-up power supply is provided. While RAM's with integral back-up power are available their additional costs and complexity are such that they also are not considered economically feasible for use in postal scales.
Because of the constraints discussed above the general practice in the postal scale industry is for the scale vendor to monitor changes in postal rates and when rates change program new PROM's with the new rates and send the new PROM's to the scale user for installation.
Because of the limitations on the amount of memory space available in a single PROM package, and the complexity of the various postal rate charts a full set of postal rate information might require 12 or more PROM packages. To provide for these PROM's each prior art scale required an electronic power supply capable of supplying the power needed by the full set of PROM's and their associated circuitry, whether or not the scale actually used the maximum number of PROM's. Further, because of memory limitations, complex and sophisticated programming techniques were necessary to reduce the postal rate data to a form which could be stored in a reasonable number of PROM packages. The complexity of the techniques used may be appreciated from consideration of those disclosed in U.S. Pat. No. 4,320,461, to Dlugos, for, Postage Value Calculator With Expanded Memory Versatility.
Thus, it is an object of the subject invention to provide a low cost postal scale.
More particularly, it is an object of the subject invention to provide a postal scale wherein the electronic power supply may be eliminated or, at least, substantially reduced in size so as to reduce the cost of the postal scale.
It is a further object of the subject invention to so reduce or eliminate power supply requirements without burdening the user with the need to monitor or maintain batteries.
It is still a further object of the subject invention to provide a postal scale wherein volatile memory may be used without increasing the total cost of the scale to provide back-up power for the memories.
It is still a further object of the subject invention to provide a postal rate memory having increased storage capacity and ease of programming.